For recognising the position and/or orientation of an object, some optical recognition systems can determine mainly the outline of the object on its support, for example on a positioning device. In order to do this, optical detection means, such as a camera, can take at least one image of the outline of the object in order to supply data signals relating to the outline of the object to a data signal processing station. In the processing station, a comparison is made between the detected outline of the object and a stored reference shape, whose position in space is known. On the basis of this comparison, the processing system can then determine a position or orientation of the object on the positioning device.
One drawback of these optical recognition systems essentially lies in the fact that the position or orientation of the object, determined by its outline, is not precise. Moreover, these recognition systems cannot be used if the object is spherical in shape, since the determination of the outline of the object is identical in any position or orientation. These optical recognition systems therefore cannot be used, for example, in systems for measuring the radiation diagram of a transmitting antenna, which is placed in a hollow spherical object, driven in rotation on a positioning device.
FR Patent No. 2 590 681 discloses a system for tracking an object provided with passive target patterns arranged on a spacecraft. The tracking system includes a proximity sensor circuit, which includes a digital imaging device and a light source transmitting light in the direction of the target patterns on the object. The object is swept with a light beam from the light source to allow the imaging device to identify the various positioning target patterns. These target patterns are different from each other and form parallel barcodes of rectangular or trapezoidal shape. There are, for example 4 of these barcodes, distributed at a distance from each other on a flat surface of the object. One drawback of this tracking system is that it does not provide a precise measurement of the position of the object relative to the sensor circuit. Moreover, it can not detect a limited angular orientation of the object on a positioning device.